Sequestering soil carbon in the low input farming systems of the semi-arid tropics – does litter quality matter?

Maintaining soil organic matter (SOM) in low input smallholder rice cropping systems worldwide is of paramount importance to maintaining livelihoods and food security. A long term rainfed lowland rice experiment tested the hypothesis that applying small (1.5 t/ha dry matter) annual additions of slowly decomposable plant materials which were grown offsite and applied prior to land preparation, could result in increased soil organic carbon, crop yield and improve the recovery of nutrients compared with plant materials of higher quality or straw retention alone. Annual leaf litter applications over 9 seasons resulted in significant increases in SOC of 39% (from 3.5 to 4.9 mg/g) in the leaf litter treatments compared to only 13 % in the noleaf litter control. In terms of rice grain production and nutrient use efficiency, leaf litter quality was an important driver. Apparent nutrient recovery of nitrogen and sulfur reflected the decomposition rate of the added residues. Sustainable farming systems will require that crop yields are stable through the maintenance of soil fertility and the balanced use of nutrients in the system. The results of this study are therefore highly significant and provide evidence that low rate, long term residue management can have profound effects

Internal efficiency, nutrient uptake, and the relation to field water resources in rainfed lowland rice of northeast Thailand

Rice-based (Oryza sativa L.) rainfed lowlands are the major cropping system in northeast Thailand. Average yields are low, which is generally explained by frequent drought events, low soil fertility, and poor fertilizer response. However, neither the relative importance of these factors nor their interaction is well understood. Therefore, we analyzed an existing database on fertilizer trials conducted between 1995 and 1997 at eight different sites in northeast Thailand with the objective to determine indigenous nutrient supplies, internal efficiencies, and recovery efficiencies of applied nutrients in rainfed lowland rice. Of particular interest was the effect of variety type (traditional) and water supply on these components. Comparison of N, P, and K concentrations in grain and straw (average N-P-K grain concentration of 11.0-2.7-3.4 g kg ; average N-P-K straw concentration of 5.2-0.9-16.4 g kg ) in the traditional-type varieties used at all trial sites with literature values showed no differences for these parameters between traditional and modern-type varieties or between irrigated and rainfed environments. In contrast, internal efficiencies of N, P, and K (average IEN: 46 kg grain per kg N uptake; IEP: 218 kg grain per kg P uptake; IEK: 25 kg grain per kg K uptake) were much lower than reported for irrigated systems, and the difference was greatest for K, which is mainly accumulated in the straw. Indigenous nutrient supply (average INS: 38 kg ha; IPS: 10 kg ha; IKS: 89 kg ha) and recovery efficiency (average REN: 0.28 kg kg ; REP: 0.13 kg kg; REK: 0.49 kg kg) were low but comparable to the lower values reported from irrigated systems. Average seasonal field water resources seemed to reduce the indigenous nutrient supply but had no or little effect on internal efficiency and recovery efficiency. We concluded that the main reason for the low system productivity without and with fertilizer in northeast Thailand is the dominant use of traditional-type varieties with low harvest indices, which was the dominant cause for the observed low internal nutrient efficiency. Therefore, intensification of rainfed systems through substantially increased nutrient inputs can be recommended only where varieties with an average harvest index of close to 0.4 or higher are available

Nutrient requirements in rainfed lowland rice

In rainfed lowland rice, nutrient status of soils is often poor, and response to applied nutrients is often unreliable. This paper seeks an improved understanding of these patterns of nutrient response, then considers likely approaches for increasing and stabilising yields of rainfed lowland rice in south and southeast Asia. At each of 78 locations across India, Bangladesh, Thailand, Indonesia and the Philippines during 1995-1997, three replicates of each of six treatments were established: (no fertiliser control (NIL), farmyard manure (FYM), phosphorus and potassium only (PK), application of nitrogen as well as P and K (NPK), a controlled-release formulation of N together with P and K (CR-NPK), and an all-nutrient dressing (ALL)). Combined analysis of variance and cluster analysis were used to examine the patterns of nutrient response. Yields obtained without applied fertiliser were not closely related to soil test values. The greatest nutrient response was to nitrogen, with NPK increasing yields from 2.25 to 4.00 t/ha on average. The effect of adding micronutrients was small, and PK was of little benefit unless N was added. But the magnitude of the N response varied substantially with water regime. We conclude that substantial yield gains are possible in rainfed systems with application of appropriate nutrients, especially if used in conjunction with cultivars suitably adapted to the target environments. (C) 1999 Elsevier Science B.V. All rights reserved

Factors affecting rice yield and fertilizer response in rainfed lowlands of northeast Thailand

Rice-based (Oryza sativa L.) rainfed lowlands are the major cropping system in northeast Thailand. Earlier research on nutrient management of rainfed lowland rice produced conflicting results with respect to inherent soil fertility, fertilizer response, and the importance of organic fertilizers. most probably because of highly variable soil quality and water resources. The objectives of this paper were to advance the understanding of soil fertility and fertilizer response in northeast Thailand and thereby provide a basic framework for improved nutrient management of rainfed lowland rice. For this purpose, we analyzed an existing database on fertilizer trials conducted between 1995 and 1997 at eight different sites in northeast Thailand, which were previously described by Wade et al. [Wade, L.J., Amarante, S.T., Olea, A., Hampichitvitaya. D., Naklang, K., Wihardjaka, A., Sengar, S.S., Mazid, M.A., Singh, G., McLaren, C.G., 1999a. Nutrient requirements in rainfed lowland rice. Field Crops Res., 64, 91-107]. Average annual rainfall across sites and seasons was 1300 rum, but half of all rainfed trials (12 of 23) experienced substantial water stress during the growing season. Average grain yield in N-omission plots was low (1.6 t ha(-1)), even when compared with that of rainfed lowlands in neighboring Lao PDR. Nitrogen was clearly the most limiting element, whereas PK treatments increased yields significantly in only 6 out of 78 observations. Average agronomic efficiency of applied N was good ( 16 kg grain kg 1 N). but highly variable among sites. Two groups of soils (i.e., sites) were separated because of their distinct differences in reaction to inorganic and organic fertilizer. Better nutrient availability improved crop performance at all field water stress levels occurring at the trial sites. However, yield reductions caused by water stress seemed to interact with the level of nutrient supply, that is, absolute yield differences between different fertilizer treatments decreased with increasing water stress. We concluded that efficient fertilizer use in rainfed rice of northeast Thailand can be achieved, but that existing uniform recommendations do not provide farmers with much useful advice. Therefore, we proposed a set of basic guidelines for improved nutrient management, which, after further efforts of all stakeholders involved, could contribute to increased system productivity. (c) 2006 Elsevier B.V. All rights reserved

Equations for Calculating N-Fertilizer Rates for Khaw Dauk Mali-105 Rice from Soil Analysis

ABSTRACT Comparisons were made to assess the reliability of 10 chemical methods for evaluating the availability of N in soils to Khaw Dauk Mali-105 rice and for calculating rates of N-fertilizer for rice. The methods studied were: (1) measuring soil organic matter by Walkley and Black's method, (2) measuring total soil N by Kjeldahl's method, (3) extracting soil N with acidified K 2 Cr 2 O 7 solution, (4) extracting soil N with basified KMnO 4 solution, (5) extracting soil N with acidified KMnO 4 solution, (6) extracting soil N with solution of CaCl 2 and K 2 SO 4 , (7) extracting soil nitrate according to Only the indices from the methods (9) and (10) gave significant relationships (at 95% confidence level) with the relative paddy yields, with Method (10) showing slight superiority over the method (9). None of the chemical methods gave significant relationships among the index and the relative dry matter and amount of N in plants. The equations for calculating rates of N fertilizer required for desired paddy yields were: (a) log (100 -y) = 2 -0.0226b -0.0374x for method (9) and (b) log (100-y) = 2 -0.00533b -0.0584x for method (10); where y is the desired grain yield (as % of maximum yield), b availability index value for soil N (in ppm N), and x rate of fertilizer N required (as kg N/rai, 6.25 rais = 1 ha). Both of the two equations gave highly significant correlation between the actual paddy yields and the predicted paddy yields. However, method (10) was more recommended than method (9) for it was more reliable than method (9) in prediction of the yield