Scientific abstracts

Effects of Three Commercial Rootstocks on Mineral Nutrition, Fruit Yield, and Quality of Salinized Tomato

Tomato (Solanum lycopersicum Mill. cv. Belladona F₁) plants were either self-rooted, self-grafted, or grafted onto the commercial rootstocks “Beaufort”, “He-Man”, and “Resistar” and grown in a recirculating hydroponic system. Three nutrient solutions differing in NaCl-salinity level (2.5, 5.0, and 7.5 dS m^–1, corresponding to 0.3, 22, and 45 mM NaCl) were combined with the five grafting treatments in a two-factorial (3 × 5) experimental design. At the control NaCl level (0.3 mM), fruit yield was not influenced by any of the grafting treatments. However, at low (22 mM NaCl) and moderate (45 mM NaCl) salinity levels, the nongrafted and the self-grafted plants gave significantly lower yields than the plants grafted onto He-Man. The plants grafted onto the other two rootstocks gave higher yields only in comparison with the nongrafted plants, and the differences were significant only at low (Beaufort) or moderate (Resistar) salinity. Yield differences between grafting treatments at low and moderate salinity arose from differences in fruit number per plant, while mean fruit weight was not influenced by grafting or the rootstock. NaCl salinity had no effect on the yield of plants grafted onto He-Man but restricted the yield in all other grafting treatments due to reduction of the mean fruit weight. With respect to fruit quality, salinity enhanced the titratable acidity, the total soluble solids, and the ascorbic acid concentrations, while grafting and rootstocks had no effect on any quality characteristics. The leaf Na concentrations were significantly lower in plants grafted onto the three commercial rootstocks, while those of Cl were increased by grafting onto He-Man but not altered by grafting onto Beaufort or Resistar in comparison with self-grafted or nongrafted plants. Grafting onto the three tested commercial rootstocks significantly reduced the leaf Mg concentrations, resulting in clear Mg-deficiency symptoms 19 weeks after planting.

Phosphorus and Potassium Fertilization do not Affect Soybean Storability

Few studies have investigated the influence of P and K fertilization on soybean [Glycine max L. (Merr.)] seed storability. The objectives were to determine the effect of P and K fertilizer rates and seed storage environments on soybean seed quality and seed carry-over potential. Seed lots were harvested from a long-term P and K trial. The plants were grown on replicated plots fertilized with one of four rates of P or four rates of K (0, 28, 56, 112 kg P₂O₅ ha⁻¹/0, 35, 70, 140 kg K₂O ha⁻¹) broadcast by hand in the fall. Seed samples were stored in four different storage environments: continuous climate controlled warehouse; continuous nonclimate controlled warehouse; nonclimate controlled warehouse and 1 mo at 12-h alternating temperatures of 4.5° and 15.5°C; and nonclimate controlled warehouse and 2 mo at alternating temperatures, with the first month at 4.5° and 15.5°C and second month at 10°C and 32.2°C. Most seed lots stored under ideal conditions were below the recommended value of 95% germination and 80% vigor following 13 mo of storage. Seed storage environments that experienced high temperature (>20°C) and relative humidity (RH) (>80%) rapidly decreased in seed viability and vigor to unacceptable levels. Phosphorus and K fertilization did not improve seed storability, although higher rates of K fertilization increased seed survival in poor storage environments for a short time. Seed producers should not store soybean seed for two growing seasons, regardless of storage environment and P and K fertilization levels in the seed production field.

Maize Response to Fertilizer and Nitrogen Use Efficiency in Uganda

Maize (Zea mays L.) is an important smallholder crop in Uganda. Yields are low because of low soil fertility and little fertilizer use. Yield response to nutrient application and economically optimal rates (EOxR, where x = N, P, or K) and N use efficiency (NUE) were evaluated. Twenty-two trials were conducted in four agroecological zones. Yield was consistently increased with N application. Mean maize yield with no N applied (N₀) was 1.79 Mg ha⁻¹ and increased by 120% with N application. Mean EONRs were 45 to 24 kg ha⁻¹ N with fertilizer use cost to grain price ratios (CPs) of 10 to 30. With N applied, the mean increase in yield due to P application was 0.28 Mg ha⁻¹ and mean EOPRs were 9 to 1 kg ha⁻¹ P with CPs of 10 to 50. Yield was not increased with K application. Profitability was greater for N than P application. Mean aboveground biomass N with 0 and 150 kg ha⁻¹ N applied was 46.3 and 94.3 kg ha⁻¹, respectively. Mean N concentration and N harvest index at the EONR were 1.60 and 63.8%, respectively, and higher than for N₀. Mean recovery efficiency, partial factor productivity, and agronomic efficiency declined with increasing N rate and were 66%, 86 kg kg⁻¹, and 41 kg kg⁻¹, respectively, at the EONR. Fertilizer N use can be very profitable, with high NUE, for smallholder maize production in Uganda, and the financial capacity of smallholders to use fertilizer will increase with reduced CP.

Potassium Mining in Indian Agriculture

Intensive production systems in India characterized by heavy removal and inadequate replenishment of nutrients resulted in depletion o f soil nutrient reserves and multiple nutrient deficiencies. For sustaining the crop productivity and to restore the soil fertility, there is a need to arrest this depletion. Clear understanding of crop nutrient balance is pre-requisite. There were many attempts to examine the potassium mining at individual plot level, long-term fertilizer experiments, state level and country level. In most of these reports, fertilizer inputs and crop removals were only considered, thus resulting in the large-scale negative K balances in Indian agriculture. In agroecosystem, K is contributed by many sources like animal manure, crop residue, compost, rice burning residue, irrigation water and rain etc. Similarly, besides crop K removal, K is lost to deeper layers by rain or irrigation water by leaching. By considering all these inputs and outputs, the holistic K balance in Indian agriculture is about 3 mt per year. This total negative balance is reduced by considering area under conservation agriculture (about 4 to 5 mha), green leaf manuring like gliricidia and other non-conventional sources of potassium being used in Indian agriculture, which reduces the overall negative balance of K to 2.8 mt annually in Indian agriculture.

Analyzing Nitrogen Use Efficiency in Long-Term Experiments in Rainfed Conditions

Rainfed soils are not only thrusty but also hungry. These soils are highly degraded, low in organic matter and are multi-nutrient deficient. Spectacular response to N application is seen in rainfed crops though application levels of nutrients are very low compared to irrigated agriculture. However, harnessing nutrient supply with optimum soil moisture availability is crucial for improving nutrient use efficiency in rainfed agriculture. This paper deals with N deficiency, nutrient consumption, nutrient uptake and N use efficiency in some long-term manorial trials going on under rainfed conditions.

Long-Term Effects of Soil Fertility Management on Carbon Sequestration in a Rice-Lentil Cropping System of the Indo-Gangetic Plains

Enrichment of soil organic carbon (SOC) stocks through sequestration of atmospheric CO₂ in agricultural soils is important because of its impacts on soil quality, agronomic production, and adaptation to and mitigation of climate change. In a 21-yr field experiment conducted under subhumid tropical conditions in India, the impacts of crop residue C inputs were assessed for the rice (Oryza sativa L.)–lentil (Lens esculenta Moench) cropping sequence. These impacts were evaluated in an experiment involving mineral fertilizers and manuring treatments on crop yield sustainability with reference to critical biomass requirements for maintenance of SOC in an Inceptisol. Application of farmyard manure (FYM) without and with mineral fertilizers increased C input and SOC concentration and stock. In comparison with the control, the 100% organic (FYM) treatment had significantly higher profile SOC (27.5 Mg ha⁻¹), and more C build up (55.0%) and C sequestration (6.6 Mg C ha⁻¹) to 1-m depth vis-à-vis the antecedent values in 1986. These parameters were also higher in 100% FYM treatment at a rate providing equivalent amount of the recommended dose of N followed by conjunctive use of FYM and mineral fertilizers. The SOC stock and rate of sequestration were positively correlated with cumulative C input, and with sustainable yield index (SYI) of upland rice and lentil. Higher grain yield (1.95 and 1.04 Mg ha⁻¹ of rice and lentil, respectively) was obtained with the application of 50% organic (FYM)+50% recommended dose of fertilizer (RDF). In comparison, higher SOC sequestration rate was measured with the application of 100% organic (FYM). For every Mg increase in SOC stock in the root zone there was 0.16 and 0.18 Mg ha⁻¹yr⁻¹ yield increase of rice and lentil, respectively. For maintaining a stable SOC level (zero change due to cropping), a minimum quantity of 2.47 Mg C ha⁻¹yr⁻¹ is required for this soil, climate, cropping system, and fertilization treatments. To achieve this quantity of C, 7.1 Mg of biomass is required to be produced every year vs. average rice and lentil yields of 1.6 and 0.7 Mg ha⁻¹, respectively. The sole application of mineral fertilizers at 50 or 100% of the RDF did not maintain the SOC stock. Thus, application of FYM (or other organics) in conjunction with mineral fertilizers is essential to maintaining and enhancing the SOC stock in the rice-based cropping systems.