Kermah M, Franke A C, Adjei-Nsiah S, Ahiabor B D K, Abaidoo R C, Giller K E
Plant Production Systems, Wageningen University, P.O. Box 430, 6700 AK Wageningen, The Netherlands.
Soil, Crop and Climate Sciences, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa.
Agric Ecosyst Environ. 2018 Jul 1;261:201-210. doi: 10.1016/j.agee.2017.08.028.
Continuous cereal-based cropping has led to a rapid decline in soil fertility in the Guinea savanna agro-ecological zone of northern Ghana with corresponding low crop yields. We evaluated the effects of cropping system and soil fertility status on grain yields and N-fixation by grain legumes and net N contribution to soil fertility improvement in contrasting sites in this agro-ecological zone. Maize was intercropped with cowpea, soybean and groundnut within a row, with a maize stand alternated with two equally spaced cowpea or groundnut stands and in the maize-soybean system, four equally spaced soybean stands. These intercrops were compared with sole crops of maize, cowpea, soybean and groundnut in fertile and poorly fertile fields at sites in the southern (SGS) and the northern (NGS) Guinea savanna. The proportion of N derived from N-fixation (%Ndfa) was comparable between intercrops and sole crops. However, the amount of N-fixed was significantly larger in sole crops due to a greater biomass accumulation. Legumes in poorly fertile fields had significantly smaller shoot N enrichment (-2.8 to +0.7‰) and a larger %Ndfa (55-94%) than those in fertile fields (-0.8 to +2.2‰; 23-85%). The N-fixed however was larger in fertile fields (16-145 kg N ha) than in poorly fertile fields (15-123 kg N ha) due to greater shoot dry matter and N yields. The legumes grown in the NGS obtained more of their N requirements from atmospheric N-fixation (73-88%) than legumes grown in the SGS (41-69%). The partial soil N balance (in kg ha) was comparable between intercrops (-14 to 21) and sole legumes (-8 to 23) but smaller than that of sole maize receiving N fertiliser (+7 to +34). With other N inputs (aerial deposition) and outputs (leaching and gaseous losses) unaccounted for, there is uncertainty surrounding the actual amount of soil N balances of the cropping systems, indicating that partial N balances are not reliable indicators of the sustainability of cropping systems. Nevertheless, the systems with legumes seem more attractive due to several non-N benefits. Our results suggest that soybean could be targeted in the SGS and cowpea in the NGS for greater productivity while groundnut is suited to both environments. Grain legumes grown in poorly fertile fields contributed more net N to the soil but growing legumes in fertile fields seems more lucrative due to greater grain and stover yields and non-N benefits.
在加纳北部几内亚稀树草原农业生态区，持续种植谷类作物已导致土壤肥力迅速下降，作物产量相应降低。我们评估了种植系统和土壤肥力状况对该农业生态区不同地点豆类作物籽粒产量、固氮作用以及对土壤肥力改善的净氮贡献的影响。玉米与豇豆、大豆和花生进行行间套种，在玉米-豇豆或玉米-花生系统中，一行玉米与两个等间距的豇豆或花生行交替排列，在玉米-大豆系统中，一行玉米与四个等间距的大豆行交替排列。这些间作作物与几内亚稀树草原南部（SGS）和北部（NGS）地点的肥沃和贫瘠田地中的玉米、豇豆、大豆和花生单作进行了比较。间作作物和单作作物之间来自固氮的氮比例（%Ndfa）相当。然而，由于生物量积累更多，单作作物的固氮量显著更大。贫瘠田地中的豆类作物地上部氮富集显著较小（-2.8至+0.7‰），%Ndfa比肥沃田地中的豆类作物更大（55-94%，而肥沃田地中为-0.8至+2.2‰；23-85%）。然而，由于地上部干物质和氮产量更高，肥沃田地中的固氮量（16-145 kg N/ha）比贫瘠田地中的更大（15-123 kg N/ha）。在NGS种植的豆类作物从大气固氮中获得的氮需求比例（73-88%）比在SGS种植的豆类作物（41-69%）更高。间作作物（-14至21）和豆类单作（-8至23）之间的部分土壤氮平衡（kg/ha）相当，但小于施用氮肥的玉米单作（+7至+34）。由于未考虑其他氮输入（大气沉降）和输出（淋溶和气态损失），种植系统的实际土壤氮平衡量存在不确定性，这表明部分氮平衡不是种植系统可持续性的可靠指标。尽管如此，由于多种非氮效益，含豆类的系统似乎更具吸引力。我们的结果表明，在SGS可选择种植大豆，在NGS可选择种植豇豆以提高产量，而花生适合这两种环境。在贫瘠田地中种植的豆类作物对土壤的净氮贡献更大，但在肥沃田地中种植豆类似乎更有利可图，因为籽粒和秸秆产量更高以及具有非氮效益。
