Uptake of NPK and yield of rainfed groundnut (Arachis hypogaea L.)

Experiments were conducted on sandy loam soils of Tirupati campus of Andhra Pradesh Agricultural University for two rainy seaons of 1980 and 1981 to study the effect of split application of NPK fertilizers on Spanish bunch groundnut. The fertilizer doses were 40 N, 20 P and 40 K kg ha^–1 in 1980 and 30 N, 10 P and 25 K kg ha^–1 in 1981.In 1980, uptake of N (48 kg ha^–1), P (7 kg ha^–1) and K (37 kg ha^–1) was maximum with the application of 10 N, 5 P and entire 40 K kg ha^–1 as basal and 30 N and 15 P kg ha^–1 at 30 days after sowing, leading to highest pod yield (0.76 t ha^–1). In 1981, application of 20 N, 10 P and 25 K kg ha^–1 as basal dose and 20 N kg ha^–1 at 30 days after seeding resulted in highest uptake of N (114 kg ha^–1), P (17 kg ha^–1) and K (58 kg ha^–1) and hence the pod yield (2.36 t ha^–1).Differences in the uptake of NPK and pod yield in 1980 and 1981 was due to variation in total rainfall and its distribution during the crop period. Rainfall was equally distributed throughout the crop period in 1981, whereas there were two prolonged dry spells of more than 40 days in 1980.     

Integrated fertilizer requirements of groundnut-wheat cropping system

Investigations were carried out in a long term field experiment from 1976 to 1982, on a loamy sand soil to find out the fertilizer requirements of groundnut and wheat grown in fixed rotation. Application of 26 kgP/ha to wheat alone was found to be sufficient for both wheat and succeeding groundnut. Application of phosphorus to both wheat and groundnut did not result in extra beneficial effect over P application to wheat alone. However, application of 26 kg P/ha to groundnut alone was not sufficient for succeeding wheat. There was no response from K application (25 kg K/ha) in either of these two crops. Increasing the dose of N from 50–150 kg/ha to wheat significantly increased the grain yield of wheat but the pod yield of succeeding groundnut were markedly lowered. Response of wheat to 150 kg N/ha was more marked when P was also applied to wheat and response was less when P was applied to preceding groundnut alone. Zinc application at 6.25 kg/ha to wheat alone resulted in significant increase in grain yield of wheat and pod yield of succeeding groundnut.     

Crop and soil nitrogen responses to phosphorus and potassium fertilization and drip irrigation under processing tomato

Shortage of water or nutrient supplies can restrict the high nitrogen (N) demand of processing tomato, leaving high residual soil N resulting in negative environmental impacts. A 4-year field experiment, 2006?C2009, was conducted to study the effects of water management consisting of drip irrigation (DI) and non-irrigation (NI), fertilizer phosphorus (P) rates (0, 30, 60, and 90?kg P?ha^?1), and fertilizer potassium (K) rates (0, 200, 400, and 600?kg?K?ha^?1) on soil and plant N when a recommended N rate of 270?kg?N?ha^?1 was applied. Compared with the NI treatment, DI increased fruit N removal by 101?%, plant total N uptake by 26?%, and N harvest index by 55?%. Consequently, DI decreased apparent field N balance (fertiliser N input minus plant total N uptake) by 28?% and cumulative post-harvest soil N in the 0?C100?cm depth by 33?%. Post-harvest soil N concentration was not affected by water management in the 0?C20?cm depth, but was significantly higher in the NI treatment in the 20?C100?cm depth. Fertilizer P input had no effects on all variables except for decreasing N concentration in the stems and leaves. Fertilizer K rates significantly affected plant N utilization, with highest fruit N removal and plant total N uptake at the 200?kg?K?ha^?1 treatment; therefore, supplementing K had the potential to decrease gross N losses during tomato growing seasons. Based on the measured apparent field N balance and spatial distribution of soil N, gross N losses during the growing season were more severe than expected in a region that is highly susceptible to post-harvest soil N losses.     

Mineral nutrition and fertilizer response of grain sorghum in India — A review over the last 25 years

Researches on the mineral nutrition and fertilizer response of grain sorghum (Sorghum bicolor (L) Moench) carried out during the last 25 years in India are reviewed here. In general, N,P,K, Fe and Mn concentrations in vegetative plant parts decreased with crop age, while the concentrations of Ca, Mg and Cu increased. The concentration of N and P increased in panicle or grains of sorghum with advance in crop age. The seasonal change for other nutrients has not, however, been studied.Accumulation and uptake of N,P, and K by grain sorghum were characterized. Usually N and P accumulated slowly compared with the rapid accumulation of K in early crop growth stage and vice-versa in later stages of growth. As against the sizable mass of N and P into panicle, K was partitioned into stalk.Fertilizer responses to N and P were observed throughout India. Improved varieties and hybrids of sorghum responded to N rates ranging from 60 to 150 kg N ha^–1, whereas a response to P application was observed up to 40 kg P ha^–1. Although responses to K application had been inconsistent, an increase in grain yield of sorghum was observed due to 33 kg K ha^–1. A balanced fertilizer schedule consisting of 120 kg N ha^–1, 26 kg P ha^–1, 33 kg K ha^–1 and 15–25 kg Zn50₄ ha^–1 is recommended for improved productivity of grain sorghum.It is concluded that systematic research efforts should be directed so as to identify problem soils showing deficiencies and toxicities of different nutrients. Characterization of the seasonal changes in the concentration and uptake of different nutrients and determination of critical concentration and hidden hunger of different nutrients in plant tissues would lead to the recommendation of balanced fertilization for different sorghum-growing regions in India.A part of the paper presented in the Silver Jubliee Conference of Indian Society of Agronomy held at H.A.U., Hissar (India) in March, 1981     

Africa — how much fertilizer needed: Case study of Sierra Leone

The quantities of nitrogen, phosphorus and potassium supplied by an average African soil cleared from bush fallow, assuming no losses, were approximated. Values ranged from 23 to 120 Kg N ha^–1, 1.8 to 12 Kg P ha^–1, 47 to 187 Kg K ha^–1, depending on type of fallow, length of fallow, drainage and extent of depletion of native supplies. Additional amounts of 4 to 5 Kg N ha^–1, 4 to 6 Kg P ha^–1 and 14 to 20 Kg K ha^–1 are obtained from the ash.Using crop nutrient removal data and approximate efficiencies of native and fertilizer N, P and K, fertilizer requirements at the reconnaissance level were estimated for selected target yields. For newly cleared uplands at cropping/fallow ratio of 2:7, N fertilizer requirements for cassava (30 t ha^–1), maize (4 t ha^–1), and sweet potato (16 t ha^–1), were 138, 98, 42 kg ha^–1 respectively. Wetland rice (4 t ha^–1) required 55 kg N ha^–1. Corresponding P fertilizer requirements for cassava, maize, sweet potato, upland rice (1.5 t ha^–1) and ground-nut (1 t ha^–1) were 190, 80, 30, 30 and 16 kg P ha^–1 respectively. Wetland rice required 83 kg P ha^–1. Substantial residual values of applied P are to be expected. Cassava required 60 kg ha^–1 of K on newly cleared land. In soils of lowered nutrient status higher N, P, and K fertilizer requirements were indicated for all crops.Land use data from Sierra Leone were used to illustrate how the total quantities of N, P and K fertilizers in a country in the forest zone of Africa can be approximated. Fertilizer needs in Sierra Leone were in decreasing order P > N K. N, P and K requirements were estimated to be 10,000 t, 20,000 t and 4,000 t respectively. The nutrient balance sheet method described in this paper is a useful tool to estimate the order of magnitude of fertilizer requirement at selected target yields for countries in Africa.     

Fertilizer responses of groundnuts (Arachis hypogae L.) under continuous intensive cultivation in the Nigerian savannah

Up until now, potash fertilization has not been part of the recommended practices for groundnut production in Nigeria and only low levels of P are recommended in line with the level of agricultural technology available to the farmer. The change from the traditional non-intensive farming practice to continuous intensive cultivation coupled with the introduction of better yielding/more-nutrient demanding crop varieties have led to a deficiency of a number of nutrients.Field experiments were carried out for 5 years (repeated on the same sites) at 8 locations in northern Nigeria to evaluate the effect of four levels of phosphorus (0, 8, 16 and 24 kg P ha^–1) and three levels of potassium (0, 20, and 40 kg K ha^–1) on yield and related parameters in groundnut. Soils at the various sites were essentially loamy sands with low levels of organic carbon and cation exchange capacity.The yield levels in the Guinea savannah were generally higher than those in the Sudan savannah but the response pattern was the same. There was significant response to applied P up to 24 kg P ha^–1. Potash applied at 20 kg K ha^–1 produced significantly higher pod yields than the control plots, but higher rates of applied K did not result in any further significant yield increase, although there was a clear consistent trend towards higher yields as the K rates increased. Phosphate X potash interaction had no significant effect on yield.Except for K, the uptake of all nutrients were significantly increased by P levels. However, only the K content of haulms and the N content of kernels were significantly increased by K application. On the average, about 58% of N, 68% of P, 19% of K, 5% of Ca and 22% of Mg were contained in the kernels while 27% of N, 23% of P, 64% of K, 83% of Ca and 69% of Mg were contained in the haulms. The implication of this is that the complete removal of groundnut residue will deplete the soil cation reverves rapidly unless these losses are compensated through fertilizer use.     

Effect of Continuous use of Sodic Irrigation Water with and without Gypsum, Farmyard manure, Pressmud and Fertilizer on Soil Properties and Yields of Rice and Wheat in a Long term Experiment

A long term field experiment was conducted for 8 years during 1994–2001 to evaluate the effect of N, P, K and Zn fertilizer use alone and in combination with gypsum, farmyard manure (FYM) and pressmud on changes in soil properties and yields of rice and wheat under continuous use of sodic irrigation water (residual sodium carbonate (RSC) 8.5 meq l⁻¹, and sodium adsorption ratio (SAR) 8.8 (m mol/l)^1/2 at Bhaini Majra experimental farm of Central Soil Salinity Research Institute, Karnal, India. Continuous use of fertilizer N alone (120 kg ha⁻¹) or in combination with P and K significantly improved rice and wheat yields over control (no fertilizer). Phosphorus applied at the rate of 26 kg P ha⁻¹ each to rice and wheat significantly improved the yields and led to a considerable build up in available soil P. When N alone was applied, available soil P and K declined from the initial level of 14.8 and 275 kg ha⁻¹ to 8.5 and 250 kg ha⁻¹ respectively. Potassium applied at a rate of 42 kg K ha⁻¹ to both crops had no effect on yields. Response of rice to Zinc application occurred since 1997 when DTPA extractable Zn declined to 1.48 kg ha⁻¹ from the initial level of 1.99 kg ha⁻¹. Farmyard manure 10 Mg ha⁻¹, gypsum 5 Mg ha⁻¹ and pressmud 10 Mg ha⁻¹ along with NPK fertilizer use significantly enhanced yields over NPK treatment alone. Continuous cropping with sodic water and inorganic fertilizer use for 8 years slightly decreased the soil pH_e and SAR from the initial value of 8.6 and 29.0 to 8.50 and 18.7 respectively. However, treatments involving the use of gypsum, FYM and pressmud significantly decreased the soil pH and SAR over inorganic fertilizer treatments and control. Nitrogen, phosphorus and zinc uptake were far less than additions made by fertilizer. The actual soil N balance was much lower than the expected balance thereby indicating large losses of N from the soil. There was a negative potassium balance due to greater removal by the crops when compared to K additions. The results suggest that either gypsum or FYM/pressmud along with recommended dose of fertilizers must be used to sustain the productivity of rice – wheat system in areas having sodic ground water for irrigation.     

Response surface analysis of the effects of seeding rates,N-rates and irrigation frequencies on durum wheat I. Grain yield and yield components

Interactive effects of nitrogen (N) rates, seeding (S) rates and irrigation frequencies on grain yield and yield components of durum wheat were studied for four years under field conditions at Tulelake, California. Each year the experiment was conducted using a split-plot design with 4 irrigation frequencies as main plots and combinations of 5 N-rates (0 to 360 kg/ha) and 5 S-rates (50 to 250 kg/ha) as subplot treatments replicated 4 times. A quadratic response surface model (RSM) was used to study the effects of these treatments on grain yield and yield components (tillers/area, kernel number/spike, kernel weight/spike and 100-seed weight). The RSM was very effective for analysis and data reduction for estimating the optimum combinations of N and S for maximizing the grain yield and yield components. The N utilization and uptake efficiency increased with each irrigation treatment and peaked at irrigation treatment C. Both N and uptake utilization efficiency decreased with each increment of N-rate.In most cases, the effect of irrigation was independent of N and S. One irrigation at tillering increased grain yield and yield components significantly over only a preplant irrigation. The response of additional irrigations were comparatively small and significant only in some cases. Both N and S had significant effects on grain yield and yield components, however, the response of N was larger than that of S. With increasing N-rate, grain yield and tiller number increased with the expected peak beyond 360kg N ha^–1 but the increments beyond 180 kg N ha^–1 were of progressively smaller magnitude. The kernel number and kernel weight per spike also increased with N-rate giving a peak between 270 and 360 kg N ha^–1. With increasing S grain yield and tiller number/area increased while kernel number and kernel weight per spike decreased progressively. It was impossible to maximize yield and yield components at a given combination of N, S, and irrigation. According to the model, grain yield and tiller number were maximized at the highest level of N and S, while kernel number and kernel weight/spike were maximized at the lowest S (50 kg ha^–1) and about 314 kg N ha^–1 under adequate water supply. On the basis of the findings of this study and output of the model, 180–360 kg N ha^–1, 150–250 kg S ha^–1 and two post-sowing irrigations (at tillering and at boot stage) in addition to a preplant irrigation was recommended for optimum yield. An additional irrigation might be required depending on the weather conditions during the grain filling period.     

Mineral nutrition of slash pine in subtropical australia. I. stand growth response to fertilization

Fertilization at plantation establishment and later age is often required to maximize stand growth of slash pine (Pinus elliottii) in subtropical Australia. A field experiment was conducted to examine stand growth response of slash pine in the first 11.5 years of plantation following (1) initial fertilization at plantation establishment with phosphorus (P) at 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg nitrogen (N) ha^–1, 50 kg potassium (K) ha^–1 and 5 kg copper (Cu) ha^–1 and (2) additional application of 40 kg P ha^–1 at age 10 years.The initial P fertilization significantly increased the stand growth in the first 9.6 years. The P banded application was more effective in improving the stand growth than the P broadcast application. Application of the N, K and Cu basal fertilizers did not affect the stand growth. Overall, 53–73% of the variation in basal area and volume growth in the first 9.6 years was explained by the initial P fertilization, indicating that P deficiency was the major factor limiting the stand growth under the experimental conditions. Optimum plantation age, at which the maximum periodical annual increment (PAI) of basal area was obtained, increased from age 10.9 to 12 years when the initial P rate increased from 11 to 90 kg P ha^–1. Application of additional 40 kg P ha^–1 at age 10 years resulted in a further improvement in the stand growth at age 11.5 years. With 66% of the variation in basal area PAI between ages 9.6 and 11.5 years, 50% was explained by the initial P fertilization and 16% by the additional P applied at age 10 years. Similarly, 51% and 12% of the variation in volume PAI were attributed to the initial P fertilization and the additional P application, respectively. This highlights the need of refertilization with P on some established stands of slash pine at later ages.     

Nitrogen and potassium requirement of pineapple in relation to irrigation in Nigeria

The investigation studied the effect of fertilization with four nitrogen levels (0, 100, 150 and 200 kg/ha), four potassium levels (0, 100, 150 and 200 kg/ha) and four irrigation treatments (0, 3, 7 and 14-day interval) on the growth and yield of smooth Cayenne pineapples. Increasing irrigation frequency increased growth parameters of number of leaves, D-leaf length and days to 50% flowering. Fruit weight was highest at N = 150 kg/ha, K = 200 kg/ ha and irrigation once a week. Higher N levels (beyond 150 kg/ha) applied after the plant crop has been harvested did not further enhance yields of the ratoon crop. For K = 200 kg/ha potential and harvested yields were reduced in all irrigation treatments when N > 150 kg/ha.     

Studies on the substitution of inorganic fertilizers with organic manure and their effect on soil fertility in rice—wheat rotation

Field studies on the substitution of N and P fertilizers with farm yard manure (FYM) and their effect on the fertility status of a loamy sand soil in rice—wheat rotation are reported. The treatments consisted of application of 12 t FYM ha^–1 in combination with graded levels of N and P. Application of fertilizer N, FYM and their different combinations increased the rice yield significantly. There was no significant response to P application. The magnitude of response to the application of 12 t FYM and its combined use with each of 40 kg and 80 kg N ha^–1 was 0.7, 2.2 and 3.9 t ha^–1 respectively. Application of 120 kg N ha^–1 alone increased the yield by 3.9 t ha^–1, and was comparable to rice yield obtained with 80 kg N and 12 t FYM ha^–1. This indicated that 12 t FYM ha^–1 could be substituted for 40 kg N as inorganic fertilizer in rice. In addition FYM gave residual effects equivalent to 30 kg N and 13.1 kg P ha^–1 in the succeeding wheat. The effect of single or combined use of inorganic fertilizers and FYM was significantly reflected in the build up of available N, P, K and organic carbon contents of the soil. The relationship for predicting rice yield and nutrients uptake were also computed and are discussed.     

Mineral nutrition of slash pine in subtropical Australia. II. foliar nutrient response to fertilization

In the previous paper, we reported the stand growth of slash pine (Pinus elliottii) during the first 11.5 years of plantation in response to (1) initial fertilization at plantation establishment with P rates of 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg N ha^–1, 50 kg K ha^–1 and 5 kg Cu ha^–1 and (2) application of additional 40 kg P ha^–1 at age 10 years. Here we present the responses in foliar nutrient concentrations of slash pine in the first 11.5 years to the initial fertilization and the additional P applied at age 10 years.Foliar N and K concentrations in the first 9.6 years of plantation decreased with the initial P rate. Application of the basal fertilizers improved foliar Cu concentration. Foliar Ca and Mg concentrations increased linearly with the initial P rate. The initial fertilization did not affect foliar Mn concentration in the first 9.6 years. Foliar P concentration increased quadratically with the initial P rate, which accounted for 77–86% of the variation in foliar P concentration. Most of the explained variation in foliar nutrient concentrations was attributable to the plantation age except for foliar P concentration. In the case of foliar P concentration, 53% was explained by the initial P rate, 31% by the plantation age and 2% by the positive interaction between the initial P rate and the plantation age. Foliar P concentration of slash pine at age 11.5 years increased quadratically with the initial P rate and linearly with the additional 40 kg P ha^–1 applied at age 10 years, accounting for 81% of the variation in the foliar P concentration. Foliar nutrient analysis indicated that P was the major limiting nutrient affecting the stand growth of slash pine in the first 11.5 years.     

Nutrient cycling in a cropping system with potato, spring wheat, sugar beet, oats and nitrogen catch crops. I. Input and offtake of nitrogen, phosphorus and potassium

Nutrient balances, defined as the difference between input with manures, fertilizers and atmospheric deposition and offtake of nutrients with harvested products in arable cropping systems, need to be positive to compensate for unavoidable losses to the environment, but should be kept at the lowest possible level to minimize emissions or unnecessary accumulation of nutrients in the soil. Data from five consecutive years are reported from a long-term nutrient monitoring experiment with three replicates, managed comparably to conventional farming practice. There were four nutrient treatments (T1–T4). Treatment T1 received chemical fertilizer only. T2 received processed organic manure, supplying 50 per cent of the crop N-requirement, supplemented by chemical fertilizers. In treatments T1 and T2 the soil was bare during winter. In T3 and T4 the crops were fertilized as in T1 and T2, respectively, but nitrogen catch crops were grown in autumn and winter. Averaged over five years, the N-balances were 46 kg N ha^-1 y^-1 in T1 and T2 and 25 kg ha^-1 y^-1 in T3 and T4 (atmospheric deposition of 44 kg N ha^-1y^-1 included). Averaged over all treatments and years, the P-balance was 7 kg ha^-1 y^-1 and the K-balance -33 kg ha^-1 y^-1. The initially high soil fertility indices for both P and K declined over the experimental period. Catch crops and organic manure did not affect crop yields or nutrient balances, except that their combination in T4 resulted in 1.5 ton ha^-1 extra dry matter yield of sugar beet roots. Between spring and harvest, potato and sugar beet showed positive N balances and the cereals negative N-balances. Sugar beet was the only crop with a positive K-balance. NPK concentrations in plant products were not systematically affected by treatments but varied considerably between seasons. At harvest, on average 63, 71, 75 and 112 kg N ha^-1 (0–90 cm) were found after sugar beet, spring wheat, oats and potato, respectively. In November catch crops accumulated on average 39 kg N ha^-1 after cereals and 33 and 5 kg ha^-1 after potato and sugar beet, respectively. In March catch crops after the cereals contained 4 kg N ha^-1 less than in autumn, but after potato and sugar beet N-accumulation in spring had increased to 49 and 29 ha N ha^-1, respectively. In spring soil mineral N (0–90 cm) varied across years from 31 to 63 kg ha^-1. The results indicate that compliance with a maximum excess of input over offtake, as imposed by future legislation, is feasible for N for cropping systems comparable to the system examined, but that the standard for P will probably turn out to be a tight one.     

Management of nitrogen by fertigation of potato in Lebanon

Reports on soil and groundwater contamination with nitrates in Lebanon and other developing countries could be related to the mismanagement of water and fertilizer inputs. The objective of this work was to determine the N requirements and N-use efficiency of a main-crop potato in Lebanon, irrigated by a drip system, compared to the farmer's practice of macro-sprinkler. In the drip irrigation, fertilizers input was as soil application at the time of sowing or added continuously with the irrigation water (fertigation). Nitrogen-fertilizer recovery was determined using ¹⁵N-labeled ammonium sulfate. Fertigation with continuous N feeding based on actual N demands and available sources allowed for 55% N recovery. For a total N uptake of 197 kg ha^–1 per season in the lower N rate, the crop removed 66 kg N ha^–1 from fertilizers. The spring potato crop in this treatment covered 44.8% of its N need from the soil and 21.8% from irrigation water. Higher N input increased not only N derived from fertilizers, but also residual soil N. Buildup of N in the soil with the traditional potato fertilization practice reached 200 kg N ha^–1 per season. With increasing indications of deteriorating groundwater quality, we monitored the nitrate leaching in these two watering regimes using soil solution extractors (tensionics). Nitrate leaching increased significantly with the macro-sprinkler technique. But N remained within the root zone with the drip irrigation. The crop response to applied N requires a revision of the current fertilizer recommendation in semi-arid regions, with an improved management of fertilizer and water inputs using fertigation to enhance N recovery.     

The effects of elemental sulphur on flowering and pod maturation in groundnut (Arachis hypogaea L.) under irrigation

Field experiments were carried out for two consecutive seasons (1980/81–81/82) in order to study the effects of elemental sulphur on flowering and pod maturation in groundnut under irrigation. Four rates of elemental sulphur (0, 50, 100, 150 kg S/ha) were used. Each rate was applied either at sowing, at maximum flowering or split equally between these two stages. Flower number per plant, total and mature pod number per plant as well as seed weight were significantly increased by sulphur when applied at sowing. Sulphur applied at flowering had no effect on these attributes. In addition, protein and total sulphur content of seeds were significantly increased by all sulphur treatments. The greatest response was obtained at or below 50 kg S/ha but above this rate there was no further increase in response.     

Long-term effects of fertilization and manuring on groundnut yield and nutrient balance of Alfisols under rainfed farming in India

Drought stress, uncertain and variable rainfall, low soil quality and nutrient deficiencies are among principal constraints for enhancing and sustaining agronomic productivity in rainfed farming in semiarid tropical regions of India. Therefore, long-term (1985–2004) effects of cropping, fertilization, manuring (groundnut shells, GNS; farmyard manure, FYM) and integrated nutrient management practices were assessed on pod yields, nutrient status and balances for a groundnut (Arachis hypogaea) monocropping system. The five nutrient management treatments were: control (no fertilizer); 100 % recommended dose of fertilizer (RDF) (20:40:40 N, P, K); 50 % RDF + 4 Mg ha^?1 GNS; 50 % RDF + 4 Mg ha^?1 FYM and 100 % organic (5 Mg ha^?1 FYM). All treatments were replicated four times. The experiment was conducted at Anantapur district, Andhra Pradesh on an Alfisol using a Randomized Complete Block design. The gap in pod yields between control and different nutrient treatments widened with increase in duration of cultivation. Use of diverse fertilizer and manurial treatments produced significantly higher yields than control (P < 0.05). Amount and distribution of rainfall during critical growth stages was more important to agronomic yield than total and seasonal rainfall. Thus, the amount of rainfall received during pegging stage (r = 0.47; P < 0.05) and pod formation stage (r = 0.50; P < 0.05) was significantly correlated with the mean pod yields. Whereas, use of diverse fertility management practices improved nutrient status in soil profiles (N, P, K, S, Ca, Mg, Zn, Fe, Mn and B) after 20 years of cropping, yet soil available N, K and B remained below the critical limits. Long-term cultivation also caused deficiency of S, Zn and B, which limited the groundnut productivity. Crop removal of N, P and K during 20 years of cultivation was more in 50 % RDF + 4 Mg ha^?1 GNS at 523, 210 and 598 kg ha^?1, respectively. With the exception of control, there was a positive nutrient balance of NPK in all other treatments. Higher positive balance of N and K were observed in 50 % RDF + 4 Mg ha^?1 GNS (616 and 837 kg ha^?1, respectively), and those of P in 100 % RDF (655 kg ha^?1) treatment. There was also a net depletion of available S, Zn, Cu and Mn, but a buildup of available Ca, Mg and Fe. Application of equal amount of GNS was as effective as or even better than FYM in terms of pod yields and nutrient buildup in the soil.     

Effect of nitrogen,phosphorus and molybdenum application on growth and symbiotic N2-fixation of groundnut in an acid sandy soil in Niger

Two field experiments were conducted in 1988 and 1989 on an acid sandy soil in Niger, West Africa, to assess the effect of phosphorus (P), nitrogen (N) and micronutrient (MN) application on growth and symbiotic N₂-fixation of groundnut (Arachis hypogaea L.). Phosphorus fertilizer (16 kg P ha^–1) did not affect pod yields. Addition of MN fertilizer (100 kg Fetrilon Combi 1 ha^–1; P + MN) containing 0.1% molybdenum (Mo) increased pod yield by 37–86%. Nitrogen concentration in shoots at mid pod filling (72 days after planting) were higher in P + MN than in P – MN fertilizer treatment. Total N uptake increased from 53 (only P) to 108 kg N ha^–1 by additional MN application. Seed pelleting (P + MoSP) with 100 g Mo ha^–1 (MoO₃) increased nitrogenase activity (NA) by a factor of 2–4 compared to P treatment only. The increase in NA was mainly due to increase in nodule dry weight and to a lesser extent to increase in specific nitrogenase activity (SNA) per unit nodule dry weight. The higher NA of the P + MoSP treatment was associated with a higher total N uptake (55%) and pod yield (24%). Compared to P + MoSP or P + MN treatments application of N by mineral fertilizer (60 kg N ha^–1) or farmyard manure (130 kg N ha^–1) increased only yield of shoot dry matter but not pod dry matter. Plants supplied with N decreased soil water content more and were less drought tolerant than plants supplied with Mo. The data suggest that on the acid sandy soils in Niger N deficiency was a major constraint for groundnut production, and Mo availability in soils was insufficient to meet the Mo requirement for symbiotic N₂-fixation of groundnut.     

Fertilizer requirement of rice-wheat and maize-wheat rotations on coarse-textured soils amended with farmyard manure

Field experiments with rice-wheat rotation were conducted during five consecutive years on a coarse-textured low organic matter soil. By amending the soil with 12t FYM ha^–1, the yield of wetland rice in the absence of fertilizers was increased by 32 per cent. Application of 80 kg N ha^–1 as urea could increase the grain yield of rice equivalent to 120 kg N ha^–1 on the unamended soil. Although the soil under test was low in Olsen's P, rice did not respond to the application of phosphorus on both amended and unamended soils. For producing equivalent grain yield, fertilizer requirement of maize grown on soils amended with 6 and 12 t FYM ha^–1 could be reduced, respectively to 50 and 25 per cent of the dose recommended for unamended soil (120 kg N + 26.2 kg P + 25 kg K ha^–1). Grain yield of wheat grown after rice on soils amended with FYM was significantly higher than that obtained on unamended soil. In contrast, grain yield of wheat which followed maize did not differ significantly on amended or unamended soils.     

A farm-level evaluation of nitrogen and phosphorus fertilizer use and planting density for pearl millet production in Niger

Mineral fertilizer use is increasing in West Africa though little information is available on yield response in farmers' fields. Farmers in this region plant at low density (average 5,000 pockets ha^–1, 3 plants pocket^–1), which can affect fertilizer use efficiency. A study was conducted with 20 farmers in Niger to assess the response of pearl millet [Pennisetum glaucum (L.) R. Br.] to phosphorus and nitrogen fertilizers under farm conditions. In each field, treatments included control, single superphosphate (SSP) only, SSP plus N (point placed near plant), and either SSP or partially acidulated phosphate rock (PAPR) plus N broadcast. N and P were applied at 30 kg N ha^–1 and 30 kg P₂O₅ ha^–1. Farmers were allowed to plant, weed, etc., as they wished and they planted at densities ranging from 2,000 to 12,000 pockets ha^–1. In the absence of fertilizer, increasing density from 2,000 to 7,000 pockets ha^–1 increased yield by 400%. A strong interaction was found between fertilizer use and density. Farmers planting at densities less than 3,500 pockets ha^–1 had average yields of 317 kg grain ha^–1 while those planting at densities higher than 6,500 pockets ha^–1 showed average yields of 977 grain ha^–1. Though phosphate alone increased yields significantly at all densities, little response to fertilizer N was found at densities below 6,000 pockets ha^–1. Significant residual responses in 1987 and 1988 were found to P applied in high-density plots in 1986. Depending on fertilizer and grain prices, analysis showed that fertilizer use must be be combined with high plant density (10,000 pockets ha^–1) or no economic benefit from fertilizer use will be realized.     

Long-term effect of continuous cropping of irrigated rice on soil and yield trends in the Sahel of West Africa

The effects of 18 years continuous cropping of irrigated rice on soil and yields were studied in two long-term fertility experiments (LTFE) at Ndiaye and Fanaye in the Senegal River Valley (West Africa). Rice was planted twice in a year during the hot dry season (HDS) and wet season (WS) with different fertilizer treatments. Soil organic carbon (SOC) under fallow varied from 7.1 g kg⁻¹ at Fanaye to 11.0 g kg⁻¹ at Ndiaye. Rice cropping maintained and increased SOC at Ndiaye and Fanaye, respectively and fertilizer treatments did not affect SOC. Soil available P and exchangeable K were maintained or increased with long-term application of NPK fertilizers. Without any fertilizer, yields decreased by 60 kg ha⁻¹ (1.5%) and 115 kg ha⁻¹ (3%) per year at Fanaye and Ndiaye, respectively. The highest annual yield decreases of 268 kg ha⁻¹ (3.6%) and 277 kg ha⁻¹ (4.1%) were observed at Fanaye and Ndiaye, respectively when only N fertilizer was applied. Rice yields were only maintained with NPK fertilizers supplying at least 60 kg N, 26 kg P and 50 kg K ha⁻¹. It was concluded that the double cropping of irrigated rice does not decrease SOC and the application of the recommended doses of NPK fertilizer maintained rice yields for 18 years.